[MPlayer-users] TV/video capture - 2 pass

[D Richard Felker III]

On Fri, Dec 06, 2002 at 11:38:29AM +0800, Mike Holland wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> 
> To get better quality video capture, it seems logical to do 2 passes.
> Compress to a reasonable size in realtime, and then do a second pass 
> without realtime constraints.
> 
>   I tried the lavc/mpeg4 built-in 2-pass, but no luck. I'm assuming it
> requires the original input for the second pass, so no good for video
> capture?
> 
>   Whats the alternative? Is there a codec that gives less compression, but
> better quality and lower CPU demand?  It would be good, but not essential,
> if the intermediate format was playable. Then I can choose to watch, or
> compress further for archiving.

Yes. vcodec=mjpeg:vqscale=2. It will use a lot of disk space, though.
However you can go back later and recompress with the normal two-pass
procedure and get the size down reasonably without much quality loss.

> ALSO: I have tried the lavc/mjpeg coder, but it doesnt produce the
> requested bitrate,
>  eg ask 1800, got [7023:63].  Tried vbitrate=9000 , got [5677:63]  No 
> errors in log.
> 
> Does that codec not support vbitrate? The HTML docs show a similar
> example.

Specifying bitrate should work, but it's not a good idea. If you plan
to transcode to mpeg4 later, you MUST have very high quality source
material, and that means you want constant qscale=2 (or at worst 3).

Rich